Yes I think you found the problem. My /etc/passwd gives me userid 10004 for web1_info. But how could this happen. Userid 10002 and 10003 don't exist. Could it be possible that i erased the info account and created it then twice? But why worked it over two months only with long loading times by loggin webmail?

is gone but it's still not possible to login webmail with the info account.
Now the owner of the other email account is back from holidays and with his account login in is no problem Do you think it's possible that we have saved too much emails (about 3500 very small sizes) and that out that exporting of the mails and recreating the account is the best way to solve this problem?

Yes with Outlook there is no problem. And when I give in the wrong password over webmail the wrong password site opens directly. Only when I use the Info account with correct password the site is loading and loading till it stops at login form. And at this time login into ispconfig site as admin is not possible too.

Hello, in the /home/admispconfig/ispconfig/lib/config.inc.php the ServerName was ok. But in the /root/ispconfig/httpd/conf/httpd.conf the ServerName line was uncomment. I changed this restarted ispconfig_server and login in was succesfull but takes about 2 minutes and ispconfig_httpd runs at 98% of CPU.
After that I restarted the server and loggin in over webmail was not succesfully.
The mail log is ok. Loggin in with the other mail account (under 100 emails the info account has about 3500) is ok every time.
That is the output of top when don't work:

I am still using v2.1 of ISPconfig and the /home/admispconfig/ispconfig/lib/config.inc.php was like this.
Do you think it's ok?
You had tell me that Updating to version 2.2 will not solve my problem so I did it not.
Do you still think so or will an update be better?

The IP adress is my only IP address and is the correct one. Do you think that the problem can be that my hostname is xxxx.serverkompetenz.net and not xxx.mydomain.de, but why works the other email it's mydomain.de too.

I will setup a new server in two weeks when the problem then is still on I will setup the other server for my domains. And then install my first server new.
But I hope it will work. Thank you for your help.